Brazil's armed forces mobilised 200,000 military personnel on a "day of action" to raise awareness of the Aedes aegypti mosquito that carries the Zika virus.
It is the first time the Army has deployed in force on home soil since the World Cup in 2014 when soldiers helped to secure Rio de Janeiro against gang violence.
The Zika epidemic is concentrated in the north-eastern state of Pernambuco, but the strategic battleground is in Rio.
A third of the troops were deployed in the city. Rio will host the Olympic Games in August, making it imperative for Brazil's Government to defeat the virus there.
"If there wasn't the Games, I don't think there would be so much worry," said Claudio Jorge Pessanha, 73, who was visited by Marines at his home near Maracana stadium, where the Olympic opening ceremony will take place.
Soldiers went door-to-door, handing out leaflets with advice on how to stop mosquitoes from breeding, as part of the nationwide campaign to reduce the spread of Zika.
But Olympic organisers have reassured athletes and guests that Zika will not pose a threat during the event.
President Dilma Rousseff appealed to the public to spend 15 minutes a week to ensure there was no standing water in their homes where mosquitoes can breed.
"If we do this, we will win the fight against the mosquito," she said. "We need everyone participating. That's what we're asking. It's important for the Olympics but it's important for pregnant women, for children, for mothers."
Last week, the World Health Organisation (WHO) said doctors were close to identifying a link between the virus and microcephaly, or impaired brain and skull development.
Two studies found evidence of the virus in the brain tissue of newborns or foetuses, indicating Zika had a tendency to infect nerve cells.
For the first time, the WHO suggested pregnant women should consider postponing travel to affected areas. So far, 26 countries have reported locally transmitted cases of the virus.